Process for the purification of coal tar

ABSTRACT

A process is disclosed for the purification of coal tar. This process comprises treating commercially available coal tar with a fatty acid ester, extracting the fatty acid ester treated coal tar with a higher molecular weight hydrocarbon such as squalane and recovering the hydrocarbon-extracted product. The coal tar thus treated is dermatologically more acceptable and clinically more effective than known coal tar extracts or preparations and can be incorporated into many dermatologically acceptable vehicles.

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[75] Inventors: Michnei lnseph Bordovsky; William Henry Woiler, both of San Antonio, Tex.

[73] Assignee: Warner-Lambert Company, Morris Plains, NJ.

[22] Filed: Mar. 22, 11972 [21] Appl. No.: 236,954

[52] US. "Cl. 208/45 [51] ilnt. Cl. (1110c 3/00 [58] Field of Search 208/39, 43, 44, 45

n11 @ct. M, 11073 Chem. Abstr. Vol. 67: 120,130x 1967 [5 7] ABSTRACT A process is disclosed for the purification of coal tar. This process comprises treating commercially available coal tar with a fatty acid ester, extracting the fatty acid ester treated coal tar with a higher molecular weight hydrocarbon such as squalane and recovering the hydrocarbon-extracted product. The coal tar thus treated is dermatologically more acceptable and clinically more effective than known coal tar extracts or preparations and can be incorporated into many dermatologically acceptable vehicles.

6 Claims, No Drawings PROCESS FOR THE lPlUlltlllFllCATllON OlF COAL TAR The present invention is concerned with a novel process and, more particularly, the present invention is concerned with a novel process for the purification of coal tar to obtain a product which has all the desirable therapeutic features of coal tar but without the staining and irritating properties.

The present invention also embraces within its scope the purified coal tar as well as compositions containing the same.

The therapeutic use of coal tar is well recognized; for example, the US. Pharmacopeia contains a monograph for this product. Commercially, coal tar is obtained as a by-product during the destructive distillation of bituminous coal. It occurs as a black viscous liquid having a characteristic naphthalene-like odor. When coal tar is incorporated into dermatologically acceptable vehicles such as ointments, lotions or solutions, it is useful in the treatment of a variety of chronic skin diseases. Because of its characteristic irritation index and because of the fact that coal tar does form a dark stain, these properties do render coal tar less desirable for application to the skin.

Accordingly, a primary object of the invention is to provide a process for extracting the dermatologically active fractions of coal tar to yield a product without the staining and irritating properties of untreated coal tar.

Another object of this invention is to provide a pro cess for preparing a coal tar extract which is therapeutically potent and can be incorporated into dermatologically acceptable dosage forms.

Yet another object of this invention is to provide dosage forms incorporating the purified coal tar of this invention.

A further object of this invention is to provide a process whereby crude coal tar can be readily purified.

Other objects and advantages of this invention will become more apparent from the following detailed description.

According to the present invention, crude coal tar is treated with a fatty acid ester followed by treating the fatty acid ester treated coal tar through an extraction process employing high molecular weight hydrocarbon such as squalane. Thus, for example, in a typical practice of this invention, a fatty acid ester is added to crude coal tar. Then squalane is added which causes the precipitation of a pitch-like substance. The supernatant liquid is recovered by separation procedures such as decantation and the pitch-like substance is discarded.

Generally speaking, for each 100 parts by weight of crude coal tar, about 25 to 50 parts by weight of the fatty acid ester is added. Also, for each 100 parts of crude coal tar, about 25 to 50 parts by weight of squalane is employed However, in order to obtain the most desirable results, it is most advantageous to maintain a one to one ratio of squalane to the fatty acid ester. For example, if 25 parts of the fatty acid ester are utilized in the initial step, 25 parts of squalane are employed in the second step. Further, to obtain optimum separation, it is critical to adhere to a definite order of treatment; that is, the coal tar is first treated with the fatty acid ester and then treated with the squalane. The resulting product thus obtained exhibits all the desirable therapeutic properties of coal tar but is less irritating and staining upon contact with the skin.

Among the fatty acid esters which can be advantageously employed in the practice of this invention are those having a total of 15 to 22 carbon atoms, for example, isopropyl myristate, isopropyl palmitate, butyl stearate and the like. While squalane is the preferred hydrocarbon, other branched chain hydrocarbons such as squalene may also be advantageously employed.

The temperature to effect the process of this invention is not critical and can be carried out at an ambient temperature, e.g., between 2030C.

Consequently, an added advantage of this process resides in that no distillation or other high temperature or pressure equipment is needed to effect the extraction.

Among the many dosage forms where the new coal tar derivative of this invention can be incorporated are, for example, shampoo, ointment, lotion, solutions and the like. These dermatologically known vehicles are well known to the pharmacists art. Generally speaking, from 1 to 10 percent by weight is incorporated into such vehicles. For example, the coal tar derivative of this invention can be prepared as an ointment by mixing 10 grams with 990 grams of Zinc Oxide Paste, U.S.P. The patient applies such an ointment liberally to the affected site two or three times daily.

In order to further illustrate the practice of this in vention, the following examples are included.

EXAMPLE 1 Into a vessel there is charged 100 grams of Coal Tar, U.S.P. While agitating, 25 grams of isopropyl myristate is added gradually until a homogenous mixture is obtained. To this is added 25 grams of squalane, with agitation, until precipitation is complete. The mixture is allowed to stand and the supernatant liquid is recovered by careful decantation. The recovered supernatant liquid has a viscosity of 10 to 50 cps as determined by the Brookfield Viscometer No. l spindle at 60 rpm and a spec. grav. at 25C of 0.88 to 0.95.

EXAMPLE 2 A new coal tar ointment is prepared as follows: 10 grams of the coal tar as prepared from Example 1 is mixed with 5 grams of polysorbate and the resulting mixture is blended with 985 grams of Zinc Oxide Paste, U.S.l.

EXAMPLE 3 A shampoo containing the coal tar of this invention is obtained by blending together the following ingredients:

Polyoxyethylene lauryl ether 20% Sodium lauryl sulfate l5-20% Coal Tar of Example 1 10% Water to make l00% EXAMPLE 4 Another ointment is prepared by blending together the following ingredients:

Fatty alcohols l0-l5% Mineral oil 8% Petrolatum 25% Sodium lauryl sulfate l-2% Coal Tar to Example l ll0% Water to make We claim: ll. A process for the purification of coal tar which comprises:

a. mixing the coal tar with afatty acid ester having 15 3. A process according to claim 1 wherein 25-50 22 carbon atoms, parts by weight of the hydrocarbon is employed for b. adding to (a) a branched chain higher molecular each 100 parts by weight of the coal tar.

weight hydrocarbon selected from the group con- 4. A process according to claim 1 wherein the hydrosisting of squalane and squalene, and carbon is squalane.

c. recovering the purified coal tar as a supernatant 5. A process according to claim 1 wherein said fatty liquid while keeping the ratio of the fatty acid ester acid ester is isopropyl myristate, isopropyl palmitate or to the hydrocarbon at 1:1. butyl stearate.

2. A process according to claim 1 wherein 25-50 6. A process according to claim 5 wherein said fatty parts by weight of fatty acid ester is added to each 100 acid ester is isopropyl myristate.

parts by weight of the coal tar. 

2. A process according to claim 1 wherein 25-50 parts by weigHt of fatty acid ester is added to each 100 parts by weight of the coal tar.
 3. A process according to claim 1 wherein 25-50 parts by weight of the hydrocarbon is employed for each 100 parts by weight of the coal tar.
 4. A process according to claim 1 wherein the hydrocarbon is squalane.
 5. A process according to claim 1 wherein said fatty acid ester is isopropyl myristate, isopropyl palmitate or butyl stearate.
 6. A process according to claim 5 wherein said fatty acid ester is isopropyl myristate. 